package info.openrocket.core.scripting;

import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import java.util.List;

/**
 * <code>ScriptEngineFactory</code> is used to describe and instantiate
 * <code>ScriptEngines</code>.
 * <br><br>
 * Each class implementing <code>ScriptEngine</code> has a corresponding
 * factory that exposes metadata describing the engine class.
 * <br><br>The <code>ScriptEngineManager</code>
 * uses the service-provider loader mechanism described in the
 * {@link java.util.ServiceLoader} class to obtain
 * instances of {@code ScriptEngineFactory} instances.
 * See {@link ScriptEngineManager#ScriptEngineManager()} and
 * {@link ScriptEngineManager#ScriptEngineManager(java.lang.ClassLoader)}.
 *
 * @since 1.6
 */
public interface ScriptEngineFactory {
	/**
	 * Returns the full  name of the <code>ScriptEngine</code>.  For
	 * instance an implementation based on the Mozilla Rhino Javascript engine
	 * might return <i>Rhino Mozilla Javascript Engine</i>.
	 * @return The name of the engine implementation.
	 */
	String getEngineName();

	/**
	 * Returns the version of the <code>ScriptEngine</code>.
	 * @return The <code>ScriptEngine</code> implementation version.
	 */
	String getEngineVersion();


	/**
	 * Returns an immutable list of filename extensions, which generally identify scripts
	 * written in the language supported by this <code>ScriptEngine</code>.
	 * The array is used by the <code>ScriptEngineManager</code> to implement its
	 * <code>getEngineByExtension</code> method.
	 * @return The list of extensions.
	 */
	List<String> getExtensions();


	/**
	 * Returns an immutable list of mimetypes, associated with scripts that
	 * can be executed by the engine.  The list is used by the
	 * <code>ScriptEngineManager</code> class to implement its
	 * <code>getEngineByMimetype</code> method.
	 * @return The list of mime types.
	 */
	List<String> getMimeTypes();

	/**
	 * Returns an immutable list of  short names for the <code>ScriptEngine</code>, which may be used to
	 * identify the <code>ScriptEngine</code> by the <code>ScriptEngineManager</code>.
	 * For instance, an implementation based on the Mozilla Rhino Javascript engine might
	 * return list containing {&quot;javascript&quot;, &quot;rhino&quot;}.
	 * @return an immutable list of short names
	 */
	List<String> getNames();

	/**
	 * Returns the name of the scripting language supported by this
	 * <code>ScriptEngine</code>.
	 * @return The name of the supported language.
	 */
	String getLanguageName();

	/**
	 * Returns the version of the scripting language supported by this
	 * <code>ScriptEngine</code>.
	 * @return The version of the supported language.
	 */
	String getLanguageVersion();

	/**
	 * Returns the value of an attribute whose meaning may be implementation-specific.
	 * Keys for which the value is defined in all implementations are:
	 * <ul>
	 * <li>ScriptEngine.ENGINE</li>
	 * <li>ScriptEngine.ENGINE_VERSION</li>
	 * <li>ScriptEngine.LANGUAGE</li>
	 * <li>ScriptEngine.LANGUAGE_VERSION</li>
	 * <li>ScriptEngine.NAME</li>
	 * </ul>
	 * <p>
	 * The values for these keys are the Strings returned by <code>getEngineName</code>,
	 * <code>getEngineVersion</code>, <code>getLanguageName</code>,
	 * <code>getLanguageVersion</code> for the first four keys respectively. For NAME, one of the Strings
	 * returned by <code>getNames</code> is returned.<br><br>
	 * A reserved key, <code><b>THREADING</b></code>, whose value describes the behavior of the engine
	 * with respect to concurrent execution of scripts and maintenance of state is also defined.
	 * These values for the <code><b>THREADING</b></code> key are:<br><br>
	 * <ul>
	 * <li><code>null</code> - The engine implementation is not thread safe, and cannot
	 * be used to execute scripts concurrently on multiple threads.
	 * <li><code>&quot;MULTITHREADED&quot;</code> - The engine implementation is internally
	 * thread-safe and scripts may execute concurrently although effects of script execution
	 * on one thread may be visible to scripts on other threads.
	 * <li><code>&quot;THREAD-ISOLATED&quot;</code> - The implementation satisfies the requirements
	 * of &quot;MULTITHREADED&quot;, and also, the engine maintains independent values
	 * for symbols in scripts executing on different threads.
	 * <li><code>&quot;STATELESS&quot;</code> - The implementation satisfies the requirements of
	 * <code>&quot;THREAD-ISOLATED&quot;</code>.  In addition, script executions do not alter the
	 * mappings in the <code>Bindings</code> which is the engine scope of the
	 * <code>ScriptEngine</code>.  In particular, the keys in the <code>Bindings</code>
	 * and their associated values are the same before and after the execution of the script.
	 * </ul>
	 * <br><br>
	 * Implementations may define implementation-specific keys.
	 *
	 * @param key The name of the parameter
	 * @return The value for the given parameter. Returns <code>null</code> if no
	 * value is assigned to the key.
	 *
	 * @throws NullPointerException if the key is null.
	 */
	Object getParameter(String key);

	/**
	 * Returns a String which can be used to invoke a method of a  Java object using the syntax
	 * of the supported scripting language.  For instance, an implementation for a Javascript
	 * engine might be;
	 *
	 * <pre>{@code
	 * public String getMethodCallSyntax(String obj,
	 *                                   String m, String... args) {
	 *      String ret = obj;
	 *      ret += "." + m + "(";
	 *      for (int i = 0; i < args.length; i++) {
	 *          ret += args[i];
	 *          if (i < args.length - 1) {
	 *              ret += ",";
	 *          }
	 *      }
	 *      ret += ")";
	 *      return ret;
	 * }
	 * } </pre>
	 *
	 * @param obj The name representing the object whose method is to be invoked. The
	 * name is the one used to create bindings using the <code>put</code> method of
	 * <code>ScriptEngine</code>, the <code>put</code> method of an <code>ENGINE_SCOPE</code>
	 * <code>Bindings</code>,or the <code>setAttribute</code> method
	 * of <code>ScriptContext</code>.  The identifier used in scripts may be a decorated form of the
	 * specified one.
	 *
	 * @param m The name of the method to invoke.
	 * @param args names of the arguments in the method call.
	 *
	 * @return The String used to invoke the method in the syntax of the scripting language.
	 *
	 * @throws NullPointerException if obj or m or args or any of the elements of args is null.
	 */
	String getMethodCallSyntax(String obj, String m, String... args);

	/**
	 * Returns a String that can be used as a statement to display the specified String  using
	 * the syntax of the supported scripting language.  For instance, the implementation for a Perl
	 * engine might be;
	 *
	 * <pre><code>
	 * public String getOutputStatement(String toDisplay) {
	 *      return "print(" + toDisplay + ")";
	 * }
	 * </code></pre>
	 *
	 * @param toDisplay The String to be displayed by the returned statement.
	 * @return The string used to display the String in the syntax of the scripting language.
	 *
	 *
	 */
	String getOutputStatement(String toDisplay);


	/**
	 * Returns a valid scripting language executable program with given statements.
	 * For instance an implementation for a PHP engine might be:
	 *
	 * <pre>{@code
	 * public String getProgram(String... statements) {
	 *      String retval = "<?\n";
	 *      int len = statements.length;
	 *      for (int i = 0; i < len; i++) {
	 *          retval += statements[i] + ";\n";
	 *      }
	 *      return retval += "?>";
	 * }
	 * }</pre>
	 *
	 *  @param statements The statements to be executed.  May be return values of
	 *  calls to the <code>getMethodCallSyntax</code> and <code>getOutputStatement</code> methods.
	 *  @return The Program
	 *
	 *  @throws NullPointerException if the <code>statements</code> array or any of its elements is null
	 */
	String getProgram(String... statements);

	/**
	 * Returns an instance of the <code>ScriptEngine</code> associated with this
	 * <code>ScriptEngineFactory</code>. A new ScriptEngine is generally
	 * returned, but implementations may pool, share or reuse engines.
	 *
	 * @return A new <code>ScriptEngine</code> instance.
	 */
	ScriptEngine getScriptEngine();
}
